Hardened antenna element cover

ABSTRACT

A hardened cover to provide weather protection (rain and thermal radiation) to an antenna element of a radar system. The antenna element includes a pair of dipoles in normal relation. Each dipole assembly includes a solid and hollow post, a cross-over wire extends between the posts to connect to a dipole arm carried on each post. The hardened cover is comprised of polytetrafluoroethylene (Teflon) filled laminated fiberglass which can be classed as an ablative material.

raw-75 Patent mi United States Fitzroy et al.

[ July 22, 1975 HARDENED ANTENNA ELEMENT COVER Inventors: Nancy D.Fitzroy, Schenectady;

Ronald L. Mann; Henry B. Gerling, both of North Syracuse; John D. Reale,Syracuse, all of N.Y.

The United States of America as represented by the Secretary of theArmy, Washington, DC.

Filed: Sept. 23, 1974 Appl. No.: 508,584

Assignee:

US. Cl 343/797; 343/872 Int. Cl. H01Q 1/42 Field of Search 343/797, 872,873

References Cited UNITED STATES PATENTS Uhrig 343/797 Primary ExaminerEliLieberman Attorney, Agent, or Firm-Lawrence A. Neureither; Joseph H.Beumer; Harold W. Hilton [57] ABSTRACT A hardened cover to provideweather protection (rain and thermal radiation) to an antenna element ofa radar system. The antenna element includes a pair of dipoles in normalrelation. Each dipole assembly includes a solid and hollow post, across-over wire extends between the posts to connect to a dipole armcarried on each post. The hardened cover is comprised ofpolytetrafluoroethylene (Teflon) filled laminated fiberglass which canbe classed as an ablative material.

2 Claims, 2 Drawing Figures PATENTEDJUL22 ms 3,896,450

FIG. I

HARDENED ANTENNA ELEMENT COVER BACKGROUND OF THE INVENTION Prior antennaelements of a radar system used ceramic type material where dielectricmaterials were required. The use of ceramics in a complex configurationwas judged to be incompatible with a nuclear environment. The mostsevere nuclear effect imposed on the assembly is thermal radiation. Amaterial investigation program was undertaken to facilitate selection ofmaterials suitable for a radome window. Three classes of material wereinvestigated; opaque materials which can char, opaque materials whichcan sublime and ceramic materials having high thermal conductivity.Analyses of ceramic materials subjected to the thermal radiationenvironment indicated that the ceramic which could best withstandthermal shock was marginal with regard to resistance to crack. Theanalyses considered only a simple model which did not contain stressriser, external loading or support boundary constraints. Due to themounting constraint and complex geometry with regard to thermal shock,ceramic type materials were judged to be inadequate for a small coverdesign.

For orientations where thermal radiation is incident on two elementposts, a large temperature differential can exist from the front to therear of each exposed post. Due to the thermal expansion property of themetal post, the posts want to bend toward those posts shaded from theradiation. Since the heated posts are connected to the relatively coolershaded posts, by means of the element cover, contact surface forces areimposed on the cover. Analyses of this thermal loading situationindicated that external loads on the element cover could be as high as3,000 pounds. This boundary loading along with the direct absorption ofthe thermal radiation requires a unique element cover design.

No information exists on the phenomenological behavior of ablativematerials subjected to combined thermal and surface force loading. Todevelop a design compatible with loading conditions it was necessary toconduct tests in a simulated thermal environment. The present cover ofpolytetrafluoroethylene filled laminated fiberglass successfullywithstood the environment. While material ablated from the externalsurfaces of the cover, little effect was experienced on the interiorwhich contained the cross-over wires. The material remained stable withno apparent warpage. This is an extremely important characteristic whenone is concerned with sealing requirements. This material exhibits aunique self-cleaning behavior in that the laminates tend to ablate awayin layers and leave a clean surface. The primary function of thefiberglass is to provide the required reinforcement while the primaryfunction of the Teflon is to provide the thermal protection.

SUMMARY OF THE INVENTION The hardened cover of the present invention isdisposed to provide weather protection (rain and thermal conditions) forelements of a radar system. The elements are a pair of dipoles in normalrelation. Each dipole assembly includes a base disposed for support of apair of posts having a dipole arm carried thereby. One post is hollowand the second post is solid. Each dipole arm is supported by respectivehollow and solid posts. The feed is carried in the hollow post and eachpost is in normal relation to the base. The dipole arms are disposed inannular relation to the base. The cross-over wires, cross over eachother in spaced relation, to connect respective arms of each dipole. Thecover of polytetrafluoroethylene filled laminated fiberglass includes asubstantially inverted conical portion and an upper member secured tothe tops of each post.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a top view of the antennaelements and cross-over wires with the cover removed.

FIG. 2 is an elevational sectional view of the antenna elements takenalong line 22 of FIG. 1, showing the cover in place.

DESCRIPTION OF THE PREFERRED EMBODIMENT As shown in FIG. 1 an antennaelement 10 for a radar includes four posts 12, 14, 16, and 18, spacedapart. A plurality of dipole arms 20, 22, 24, and 26 are secured toposts 12, 14, 16, and 18, respectively. A base 28 supports the posts.Posts 12 and 14 are solid and posts 16 and 18 are hollow. A firstcross-over wire 30 connects diopole arms 20 and 24. A second crossoverwire 32 crosses under wire 30 and connects dipole arms 22 and 26. Thecross-over wires are secured to the solid posts by screws 34 and to theconductor 33 in the hollow posts by screws 36. Conductor 33 is the feedfor the antenna element.

To protect the antenna element against rain and thermal radiation, acover assembly 37 is positioned atop the antenna element. Cover assembly37 includes a lower substantially frusto-conical member 38 having anannular flanged portion 40, and an upper flat plate 42. Plate 42 andsection 38 are secured to the antenna element by screws 44. The postsare provided with a cut back portion 46, as shown in FIG. 2, to receivethe conical surfaces of frusto-conical member 38 therebetween.

The cover assembly consists of glass cloth impregnated with apolytetrafluoroethylene resin compound or binder. Some suchpolytetrafluoroethylene filled laminated fiberglass are identified asDilecto sheets by the Budd Company, and Fluorglas by Dodge Industries.

We claim:

1. In an antenna element including a pair of dipole assemblies, covermeans for protecting said element against rain and thermal radiationcomprising:

a. a frusto-conical member mounted on top of said dipole assemblies;and,

b. an upper plate mounted on top of said frustoconical member;

c. said plate and said frusto-conical member comprised ofpolytetrafluoroethylene filled laminated fiberglass.

2. An assembly as set forth in claim 1 wherein said dipole assembliesinclude a pair of dipoles each comprised of a solid and hollow posthaving a dipole arm extending therefrom and a cross-over wire extendingfrom each said hollow and solid post, said cross-over wires beingdisposed in crossed, spaced relation.

1. In an antenna element including a pair of dipole assemblies, covermeans for protecting said element against rain and thermal radiationcomprising: a. a frusto-conical member mounted on top of said dipoleassemblies; and, b. an upper plate mounted on top of said frusto-conicalmember; c. said plate and said frusto-conical member comprised ofpolytetrafluoroethylene filled laminated fiberglass.
 2. An assembly asset forth in claim 1 wherein said dipole assemblies include a pair ofdipoles each comprised of a solid and hollow post having a dipole armextending therefrom and a cross-over wire extending from each saidhollow and solid post, said cross-over wires being disposed in crossed,spaced relation.